It is known that exhaust gas aftertreatment systems of internal combustion engines may be equipped, among other aftertreatment devices, with a lean nitrogen-oxides trap (LNT) which is provided for trapping nitrogen oxides (NOx) contained in the exhaust gas.
These aftertreatment devices are subjected to periodical regeneration events in order to release the NOx from the Lean NOx traps. A regeneration event may be operated by switching the engine from a conventional lean-combustion mode to a rich-combustion mode. When the engine is switched to the rich-combustion mode, the NOx stored on adsorbent sites of the LNT reacts with reductants contained in the exhaust gas, such as unburned Hydrocarbons (HC), and are desorbed and converted to nitrogen (N2) and ammonia (NH3).
In some aftertreatment system configurations, the LNT may be followed by a passive (or in-situ) NH3 storage device, such as a selective catalytic reduction system (SCR) or a selective catalytic reduction system on particulate filter (SCRF), which stores and then uses the ammonia generated by the LNT during the regeneration events as a reductant for reducing NOx contained in the exhaust gas downstream of the LNT, without requiring external NH3 sources.
Since the amount of ammonia generated by the LNT depends on many parameters, a need exists of a method that provides a proper and accurate determination of the amount of NH3 which is produced by the LNT during the regeneration event and which may accumulate into the NH3 storage device during the regeneration event of the LNT.